Beginner problem: casting in opCmp override

[Ugbar Ikenaki]

Thanks for the quick response!

Here is the initialization code for my Rat struct. I created a 
GCD function that I've tested to work fine:

import std.stdio, std.exception;

struct Rat {
	private long n; //Numerator
	private long d; //Denominator
	
	
	
	public this( long numerator, long denominator ) {
		enforce( denominator != 0, "Error. Denominator can not be 0. 
(Rat.this)");
		
		//Default 0-value Rat object
		if( numerator == 0 || numerator == -0 ) {
			n = 0;
			d = 1;
			
		} else {
			//Assign appropriates signs (+ / -) to numerator
			// -x/-y
			if( numerator < 0 && denominator < 0 ) {
				numerator = -numerator;
				denominator = -denominator;
			// x/-y
			} else if( numerator > 0 && denominator < 0 ) {
				numerator = -numerator;
				denominator = -denominator;
			}
			
			//Find GCD of numerator and denominator
			long gcd = gcd( numerator, denominator );
			
			//Return reduced fraction of numerator and denominator 
(invariant)
			n = numerator / gcd;
			d = denominator / gcd;
		}
	}



The following is the code to override the opCmp function:


	int opCmp( Object o ) {
		Rat other = cast(Rat) o;
		
		long num1 = n;
		long den1 = d;
		long num2 = other.n;
		long den2 = other.d;
		
		//If denominators are not equal to each other...
		if( den1 != den2 ) {
			//Set denominators equal to each other (with corresponding 
numerators)
			num1 *= den2;
			den1 *= den2;

			if(den2 < den1) {
				num2 *= (den1 / den2);
				den2 *= (den1 / den2);
			} else {
				num2 *= (den2 / den1);
				den2 *= (den2 / den1);
			}
			
			//Return opCmp int value (-1, 0, 1)
			if( num1 - num2 < 0 ) {
				return -1;
			} else if( num1 - num2 == 0 ) {
				return 0;
			} else {      //if( num1 - num2 > 0 )
				return 1;
			}
			
		//If denominators are equal to each other...
		} else {
			//Less than
			if( num1 - num2 < 0 ) {
				return -1;
                         //Equal to
			} else if( num1 - num2 == 0 ) {
				return 0;
                         //Greater than
			} else {      //if( num1 - num2 > 0 )
				return 1;
			}
		}
	}